This invention relates to mass spectroscopy and in particular to components for manipulation of charged particles in, for example, mass spectrometers.
Mass spectrometry is an analytical methodology used for quantitative chemical analysis of materials and mixtures of materials. In mass spectrometry, a sample of a material, usually an organic or inorganic or biomolecular sample, to be analyzed called an analyte is broken into electrically charged particles of its constituent parts in an ion source. The particles are typically molecular in size. Once produced, the analyte particles are separated by the spectrometer based on their respective mass-to-charge ratios. The separated particles are then detected and a mass spectrum of the material is produced. The mass spectrum is analogous to a fingerprint of the sample material being analyzed. The mass spectrum provides information about the masses and, in some cases, quantities of the various analyte ions that make up the sample. In particular, mass spectrometry can be used to determine the molecular weights of molecules and molecular fragments within an analyte. Additionally, to some extent mass spectrometry can identify molecular structure and sub-structure and components that form the structure within the analyte based on the fragmentation pattern when the material is broken into particles. Mass spectrometry has proven to be a very powerful analytical tool in material science, chemistry and biology along with a number of other related fields.
There are challenges in building a high performance mass spectrometer such as a mass spectrometer having high sensitivity, high resolution, high mass accuracy, and wide dynamic range. One challenge is how to efficiently use sample material, which includes maximizing ionization efficiency and then efficiently transmitting formed ions into a mass analyzer.
However, for many mass spectrometric applications, high loss occurs when transmitting ions from a high-pressure region where ions are usually generated, to a low pressure region in the mass analyzer. This ion loss is a result of relatively long distances needed for differential pumping stages and ion-molecule collision with a background gas when ions travel this distance. This is especially found in situations where ions are generated at atmospheric pressure or relatively high gas pressure. Such applications include, for example, electrospray ionization mass spectrometer (ESI-MS), atmospheric pressure chemical ionization mass spectrometer (APCI-MS), inductively coupled plasma mass spectrometry (ICP-MS) and glow discharge mass spectrometry (GDMS).
Ion optic devices have been used for transmitting charged particles and manipulating a beam of charged particles. In particular, ion optic devices have been used, for example, for focusing or defocusing of a beam of charged particles and for changing the particle energy and the energy distribution of the beam. Prior approaches to the above devices generally can be divided into two categories. Some known devices use magnetic fields or electrostatic fields in various configurations. Such devices include, for example, electrostatic einzel lenses and electrostatic or magnetic sector fields and multipole lenses. Other known devices use a radio frequency (RF) electrical field such as that employed in RF multipole ion guides and RF ion funnels, which consist of a series of ring electrodes. In comparison to those approaches that employ an electrostatic field, ion optic devices using an RF field offer significantly higher transmission efficiency and the ability to modify ion energy by collisional cooling when utilized with a gas of intermediate pressure. Another advantage is the use of the RF field for collision induced dissociation (CID) to produce fragment species from molecular ions, which is an important tool for study of molecular structure. In commercial mass spectrometric instruments, RF multipole ion guides are widely used.
In collision induced dissociation, a multipole ion guide also acts as a collision cell. When molecular or polyatomic ions collide with the background gas (normally an inert gas), a portion of the translation energy of the ions converts into activation energy that is sufficiently high enough and certain molecular bonds are broken. The fragment pattern produced characterizes the original molecule and provides information about its structure. In such applications, a multipole ion guide is placed between two mass spectrometers to form a tandem MS and is used to confine both the parent ions and the fragments of the parent ions otherwise referred to as daughter ions. Confinement of the ions is generally realized by use of an oscillating electrical potential field.
A conventional electric RF multipole ion guide may be constructed by using several (even numbers) circular electrically conductive rods of identical geometric dimension arranged parallel at a circumference of radius r0, as shown in FIG. 1. When radio frequency voltages of opposite polarities, U+Vcos(xcfx89t) and xe2x88x92[U+Vcos(xcfx89t)] are alternately applied to the adjacent rods, a symmetric RF field is established inside of radius r0 as can be derived from the electric potential field shown in FIG. 2. In accordance with the numbers of rods, such fields are classified as quadrupole, hexapole and octopole, and so forth, for four rods, six rods and eight rods, respectively. At any cross section of the RF multipole field, the potential distribution is a function of time and is characterized by the RF frequency xcfx89.
One embodiment of the present invention is an apparatus comprising a hollow first element and a hollow second element. The second element is disposed within the first element. The second element has at least two openings in a wall thereof. The openings are elongated and radially disposed with respect to the axis of the second element. The length of the openings is at least about 20% of the length of the second element. The first element and the second element each are adapted independently to receive a voltage to generate within the second element an oscillating electric potential field having predetermined characteristics.
Another embodiment of the present invention is an apparatus comprising a tubular first element and a tubular second element. The second element is coaxially disposed within the first element. The second element has from two to eight openings in a wall thereof. The openings are elongated and radially disposed with respect to the axis of the second element. The length of the openings is at least about 20% of the length of the second element. The dimensions of the openings are approximately equal. The first element and the second element each are adapted independently to receive a voltage to generate within the second element an oscillating electric potential field having predetermined characteristics.
Another embodiment of the present invention is an apparatus comprising a tubular first element and a tubular second element. The second element is coaxially disposed within said first element and has from two to eight openings in a wall thereof. The openings are elongated and radially disposed with respect to the axis of the second element and the length of each of the openings is at least about 20% of the length of the second element. The dimensions of the openings are approximately equal. The ends of the first element and the second element are not coplanar. The first element and the second element are each adapted independently to receive a voltage to generate within the second element an oscillating electric potential field having predetermined characteristics.
Another embodiment of the present invention is a mass spectrometry apparatus comprising an ion source for producing ions, an apparatus for manipulating the ions, an electrical source for independently applying voltages to elements of the apparatus and a mass analyzer. The apparatus for manipulating ions generally is placed between the ion source and the mass analyzer. The apparatus for manipulating the ions comprises a tubular first element and a tubular second element. The second element is coaxially disposed within the first element. The second element has two to eight openings in a wall thereof wherein the openings are elongated and radially disposed with respect to the axis of the second element. The length of each of the openings is at least about 20% of the length of the second element. The first element and the second element each are adapted independently to receive a voltage to generate within the second element an oscillating electric potential field having predetermined characteristics.
Another embodiment of the present invention is a method for manipulating charged particles. Charged particles are directed from a source thereof into a zone. A first electrical potential is generated in the zone. Simultaneously, a second electrical potential is generated outside the zone. The second electrical potential penetrates into the zone and combines with the first electrical potential to form an oscillating electrical potential field having sub-fields of alternating polarity that causes the charged particles to execute harmonic motion.
Another embodiment of the present invention is a method for creating an oscillating electrical potential field having sub-fields of alternating polarity. A first electrical potential is generated in a zone. Simultaneously, a second electrical potential is generated outside the zone. The second electrical potential penetrates into the zone and combines with the first electrical potential to form an oscillating electrical potential field having sub-fields of alternating polarity.
Another embodiment of the present invention is a method for creating an oscillating electric potential field having sub-fields of alternating polarity. A first voltage is applied to a second element of an apparatus comprising a first element and the second element. The second element is coaxially disposed within the first element and the second element has at least two openings in a wall thereof. The openings are elongated and radially disposed with respect to the axis of the second element. The length of the openings is at least about 20% of the length of the second element and the dimensions of the openings are approximately equal. A second voltage is applied to the first element to generate within the second element an oscillating electric potential field having sub-fields of alternating polarity. At least one of the voltages has an oscillating voltage component.
Another embodiment of the present invention is a method for transporting charged particles. Charged particles are directed from a source thereof into a tubular second element of an apparatus comprising a tubular first element and the tubular second element. The second element is coaxially disposed within the first element and has at least two openings in a wall thereof. The openings are elongated and radially disposed with respect to the axis of the second element. The length of the openings is at least about 20% of the length of the second element. The dimensions of the openings are approximately equal. Voltages are independently applied to the first element and the second element to generate an oscillating electric potential field having predetermined characteristics sufficient to confine the charged particles in the second element during transportation through the second element.
Another embodiment of the present invention is an apparatus such as mentioned above employed in systems in which charged particles are transferred through one or more vacuum stages or chambers while allowing neutral background gas to be pumped away. In that regard the present apparatus may be disposed between two or more vacuum chambers.
Another embodiment of the present invention is a method for cooling charged particles. In the method the charged particles are directed from a source thereof into a tubular second element of an apparatus, which comprises a tubular first element and the tubular second element. The apparatus is held under a neutral gas background usually at an intermediate pressure. The second element is coaxially disposed within the first element The second element has at least two openings in a wall thereof wherein the openings are elongated and radially disposed with respect to the axis of the second element. The length of each of the openings is at least about 20% of the length of the second element. The pressure of the neutral gas is sufficient such that the mean free path of the neutral gas is smaller than the length of the second element. Voltages are applied independently to the first element and the second element to generate an oscillating electric potential field having predetermined characteristics sufficient to bring into harmonic motion the charged particles passing through the second element.
Another embodiment of the present invention is a method for subjecting charged particles to collision induced dissociation. The charged particles from a source thereof, are directed into a tubular second element of an apparatus comprising a tubular first element and the tubular second element, which is coaxially disposed within the first element. The apparatus is held under a neutral gas background usually at an intermediate pressure. The second element has at least two openings in a wall thereof wherein the openings are elongated and radially disposed with respect to the axis of the second element. The length of each of the openings is at least about 20% of the length of the second element. The pressure of the neutral gas is sufficient such that the mean free path of the ions is smaller than the length of the second element. Voltages are applied independently to the first element and the second element to generate an oscillating electric potential field having predetermined characteristics sufficient to confine the charged particles passing through the second element so that the particles undergo collision induced dissociation.